Mattresses for sofa beds have been noted for providing poor sleeping comfort due in large part to the necessity of being folded into a limited space when converting the sofa bed to the sofa mode. In order to permit folding into the limited space requirements of the sofa bed frame, the mattresses have been constructed with a relatively minimal depth dimension which detracts from the comfortability of the mattress when used in the bed mode of the sofa bed.
More recently, some sofa bed mattresses have been constructed with a conventional arrangement of coil springs to give, for example, a seven inch mattress height when unfolded into the bed mode. However, in order to permit the mattress to be folded and compressed into the limited space of the frame when converted to the sofa mode, a special, large, "big box" mechanism for folding the bed and mattress must be used which results in an additional disadvantage of requiring the front rail of the sofa bed to be raised to accommodate the large mechanism. These requirements not only increase the cost of manufacture but also prevent desired low rail styling to be achieved. While it is possible to construct and arrange the coil springs to have a high degree of flexibility to allow the mattress to be compressed and folded into the limited space of the frame with a conventional size linkage mechanism, the resulting mattress is too soft to provide desired comfort when unfolded for use as a sleep mattress.